Dave wrote:
well DUH! obviously if you want to measure swr on a 450 ohm ladder line you
don't use a 50 ohm bird!

Yes, now you are getting it. If you want to measure SWR on a 75 ohm
coax line, you don't use a 50 ohm Bird. I couldn't have said it
better myself.
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73, Cecil http://www.qsl.net/w5dxp